Bushing for the production of thermoplastic fibers



Jan. 5, 1965 P. H. MITCHELL 3,164,453

BUSHING FOR THE PRODUCTION OF THERMOPLASTIC FIBERS Filed Dec. 8, 1960 2 Sheets-Sheet 1 FIGJ IN V EN TOR. P40 Ii M/TCl/EIL A TI'ORNEY Jan. 5, 1965 P. H. MITCHELL BUSHING FOR THE PRODUCTION OF THERMOPLASTIC FIBERS Filed Dec. 8, 1960 2 Sheets-Sheet 2 INVENTOR. P404 1% flfll'C/IAZA ,1 58 BUSHING Eon THE PRODUCTION OF THERMOPLASTIC FmERs Paul H. Mitchell, Shelbyville, Ind., assignor to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 8, 1960, Ser. No. 74,688 1 Claim. (Cl. 65-42) This invention is concerned with a metal feeder for the production of thermoplastic fibers, and it has particular relation to a simple method of constructing a feeder and support for it to enable it to operate more efficiently in the formation of thermoplastic fibers such as glass fibers. In the glass fiber art such feeders are referred to as bushings, and the description of the invention in the specification and claim will employ the term bushing as a generic term for metal feeders.

It is known to employ electrically heated, metal alloy bushings in apparatus suitable for manufacturing glass fibers. The bushings have a plurality of circular orifices in them through which molten glass flows in the form of streams. The streams are subsequently attenuated into fibers. The bushing is made of an alloy capable of Withstanding the temperature of molten glass, and it is capable of being heated to temperatures approximating fiber forming temperature-of the glass by the passage of electric current through it. The glass is heated in the bushing by conduction of the heat from the bushing. One alloy which has been employed to manufacture bushings is a platinum-rhodium alloy containing about 87 to. 90 percent from about 0.03 to 0.35 inch and the orifices are arranged in rows extending along the length of the bushing, there being, for example, 1 to 20 rows having30 to 50 or more tips in each row. Terminals in the form of strips of the platinum alloy are weldedto oppositeends of the bushing. These terminals are connected to bus bars to supply current to the bushing. This type of bushing has been employed in the manufacture of fine, staple fibers according to the process shown in US. Patent No. 2,489,243 and in the manufacture of continuous strands according to the process shown in US. Patent No. 2,133,238. I

The critical point in the fiber forming process is where the fibers are pulled from the bushing tips and stretched out to form the filaments. The molten glass forms as an inverted cone hanging from the bushing tip and the filament is pulled from the apex of the cone. The glass-is heated in the bushing to a temperature at which it is quite fluid in order to insure that the glass is in a highly refined state. At this temperature, it is much too fluid for fiber forming, and it must be cooled by the timeit' reaches the cones so that it is viscous enough for fiber forming. Some cooling of the glass is accomplished as it passes through the bushing tips and the glass is cooled to fiber drawing temperature as it is exposed to the atmosphere while it is suspended in the cone. Artificial cooling of the glass in the cone may also be employed.

One of the problems in the formation'of fibers according to either of the above processes is to maintain the temperature of the bushing and the temperature of the glass passing through the orifices in the bushing uniform throughout the length of the bushing. If the temperature of 'the' bushing varies 'alongits length, the temperature'and' viscosity of the glass passing through orifices in the bushing will differ along-*the'lcngth ofthe bushing and the diameter of'thefibersformedfrom the streams passing through theofifices willthen be'diifer'ent'. This is undefiber formingpro'ce'ss; It-isespecially undesirablein 'the process for forming short staple fibers; for in order to obtain maximum production in such process, it is necessary that the primary filaments from which the short staple fibers are formed are of maximum, uniform diameter. It is undesirable in a continuous strand process for in this case the yarn formed does not conform to fiber diameter specifications.

Each bushing which is employed in the fiber forming processes is manufactured as a bushing unit which is made up of the platinum alloy bushing, a metal support surrounding the bushing and refractory insulation between the support and the bushing. The support is provided with suitable lugs to permit the unit to be mounted underneath and in line with an opening in the forehearth. When a bushing becomes worn out or damaged, the entire bushing unit is simply replaced with a new bushing unit.

In the past the bushing units have been constructed by cementing properly shaped blocks of refractory material into place between the support and the bushing. This is time-consuming and requires the skill of a bricklayer to properly fit the refractory blocks into the space between the bushing and support and seal them completely so as to provide the proper insulation. This method of forming the bushing unitis also undesirable for it requires the stocking of many different sizes of refractory blocks for the different size bushings which are employed in the different processes. This type of construction is further unsatisfactory, for if the blocks are not perfectly positioned and all crevices completely sealed, there are heat leaks in the insulation and local cold spots appear in the bushing which result in non-uniformity of glass temperature,

viscosity and fiber diameter along the length of the bushing. This is especially true of the fit of the refractories around cooling tubes and thermocouple Wires which are unit which is simple .and quick, does not require the inventory of a substantial number of refractory block sizes and which results in a completely and uniformly sealed and insulated bushing unit. It is also an object of this invention to provide a bushing unit in which the bushing canbe heated uniformly throughout its length,

In accordance with the invention these objects are achieved by constructing the bushing in a particular manher. The bushing is constructed by positioning the bushing and supporttherefor in proper spaced relation to each other, pouring an aqueous slurry of a castable refractory material in between the two elements and drying the refractory material to set it and adhere the bushing and support together. The bushing unit is then heated to remove all the moisture from the refractory material. The bushing unit as thus prepared is ready for installation in the fiber forming process. The heat of the glass flowing through the bushing causesthe refractory material in the: bushing unit to be finally set.

The invention is further described in conjunction with the drawings in which:

FIG. 1 is an elevation of a fiber forming process illustrating the bushing unit in combination with other fiber forming apparatus;

FIG. 2 is a plan view of the bushing unit;

FIG. 3 is a view in section taken along lines II-II of FIG. 2 with portions of the glass furnace forehearth added in section;

FIG. 4 is a view in section taken along lines III-III of FIG. 2; and H FIG. 5 is an inverted sectional view similar to FIG. 4 illustrating the method of manufacturing the bushing unit.

In FIG. 1 of the drawing there is shown a forehearth of -a glass melting furnace containing a supply of molten glass 11 and having a bushing unit 12 attached to the bottom of the forehearth and centered under an opening in the bottom of the forehearth. The bushing unit is composed of a bushing 13 made of a platinumrhodium alloy containing approximately 90 percent by weight platinum and the bushing is trough-like in shape. The bushing is heated by electric current which is passed through terminals 14 connected to the ends of the bushing. The bottom face of the bushing is provided with a series of orifices with a hollow tip 15 defining and extending downwardly from-each orifice. The tips 15 are formed in a number of rows so that there are a plurality of tips extending from the bushing.

Glass filaments 19 are pulled from cones of glass 20 which are suspended from each of the tips 15. These filaments are pulled ata very high rate of speed, i.e. 5,000 to 20,000 feet per minute and wound on a rapidly rotating forming tube 22. The filaments are grouped into a strand 24 as they pass over a gathering guide 26 prior to their being wound on the forming tube 22. Usually a size made up of a liquid binder and lubricant, such as a combination of starch and vegetable oil, is applied to the filaments as they pass over a rotating roller 27 mounted in a container 28 holding a supply of the size. As the strand 24 is wound on the tube 22, it is rapidly traversed along the length of the tube by means of a suitable rotating traverse mechanism 30.

The bushing unit of the present invention is shown in further detail in FIGS. 2 to 4. The bushing 13 has a flange extending in a horizontal plane from the tops of the sides of the bushing. The flange is continuous and extends completely around the bushing. Mounted directly underneath the flange in touching relation therewith is a stainless steel cooling tube 36 which enters the bushing unit from one side through an opening 37 in the supporting frame and travels around the bushing and exits from the unit at the opening 37 where it enters. This cools the flange of the bushing so that when the bushing unit is in place, the glass which tends to seep sideways from the forehearth into the space between the bushing flange and the forehearth is cooled and solidified at point 39 just above the flange of the bushing 13. Thus, a glass seal is formed between the bushing unit 12 and the forehearth 10.

The supporting member for the bushing unit is a manganese-bronze alloy frame 40 which is also troughlike in shape and is of greater size than the bushing. The frame 40 is open at the bottom to permit the bottom of the bushing 13 to be exposed through this opening.

The frame has two lugs 42 extending from its ends, and

these lugs are drilled to provide for the aligning of the lugs to the furnace forehearth supporting structure 43 TiO 1.2% Fe O 7.3% CaO, 0.2% ,MgO, 1.2% alkalies and 0.1% ignition loss. The castable refractory material is poured as an aqueous slurry into the space between the bushing 13 and the frame 40 and completely fills this space, surrounding closely the thermocouple 44 and cooling tube 36, so as to provide complete and uniform insulation between the bushing and the frame. It is unportant that the refractory material fits closely around all parts of the bushing unit so that there are no voids which will provide paths for' excessive heat loss from localized portions of the bushing. v

The method of producing the bushing unit 12 can be described in conjunction with FIG. 5. A sheet of tin 50 is placed on a table 52 or other flat surface. The bush ing 13 is then turned upside down and placed with the flange 35 on the surface of the tin sheet 50. The thermocouple 44 has previously been'welded to the side of the bushing. The top surfaces of the frame are provided with a coating of sillimanite cement which is approximately inch in thickness and the frame is then turned upside down and placed in surrounding relation to the bushing 13 on the tin sheet 50. The bottom of the bushing is then level with the bottom of the frame 40. The

"bottom of the bushing, especially the tip section, is cov by means of dowels. The outer edges of the flange 35 are spaced from the inner walls of the frame 40. A thermocouple 44 is welded to one side wall of the bushing at about the mid-point along the length of the bushing and the thermocouple 44 extends from the bushing out through opening 46 in the frame 40.

In between the frame 40 and the bushing 13, there is poured a castable refractory material 47 which fits closely against all, the surfaces of thenbushing 13, tube 36, thermocouple 44 and frame 40. his material is a refractory material which is designed for withstanding the temperatures of operation of the bushing. A suitable material is an aluminum silicate powder capable of. withstanding a temperature of 2600 F. and which is commerciallyravailable as a castable refractory .material.

The refractory material has the following chemical analysis in percent by weight: 36.7% SiO 52.6% A1 0 0.7%

ered with masking tape. The cooling tube 36 is then po sitioned on the flange 35 of the bushing13 and is held in place by gravity. The cooling tube 36 and thermocouple 44 are fitted through openings 37 and 46 respectively in the frame 40.

The castable refractory material 47 is then mixed with a suitable amount of water to a trowelable consistency. The space between the bushing and the frame is filled by pouring and troweling the casta'ble refractory material in the opening between the bottom of the bushing and the bottom of the frame. The castable refractory material flows to all sections of the space and completely and uniformly fills it. The castable refractory material is leveled off so that it is level with the bottom of the bushing and the frame.

This assembly is allowed to air dry for about one hour. This hardens the refractory material and adheres 'all of the elements of the bushing unit to each other through the adhesive nature of the refractory material. The unit is then baked at about 200 F. until all mois ture is removed from the castable refractory material This will take about three to four hours. The baking or prefiring removes all of the water and prevents steaming and cracking of the bushing unit when it is subjected to the heat of the fiber forming operation. The baking or prefiring also minimizes the shrinking of the castable refractory material and permits a tight fit between all of the elements of the bushing unit. The bushing unit as thus manufactured is ready for installation under a forehearth. The castable refractory material is finally and completely set as the bushing unit is exposed to the heat of the molten glass flowing through it.

As can be seen from the above description, the present invention provides a simple method of making a bushing unit. This method avoids the necessity for stocking many sizes of refractory blocks and avoids the difficulties involved when the blocks are of improper size and do not fit properly in between the bushing and frame of the bushing unit. The bushing unit is easier and chea er to assemble than prior art bushing units. It has also been forming has resulted from use of the bushing units pre-- pared as described above. 1

, 5 v Although the presentinvention has been described with respect to specific details of certain, embodiments thereof, it is not intended that such details serve as limitations upon the scope of the invention except insofar as set forth in the accompanying claim.

I claim: A bushing unit for producing thermoplastic fibers which comprises a bushing, a frame in spaced relation to the bushing, and a mass, of refractory material cast in situ between the bushing and the frame forming a rigid sealed unit, the bushing and the frame being adhered to the refractory material and thermally insulated from 1 each other.

References Cited in the file of this patent UNITED STATES PATENTS Cook Nov. 23, 1915 Frink July 16, 1929 Warren Oct. 15, 1929 McGraw Dec. 22, 1931 Esser Dec. 23, 1941 Norton Oct. 24, 1950 Russell Oct. 13, 1959 Drummond et a1. Aug. 23', 1960 FOREIGN PATENTS,

Australia Aug. 28, 1958 

